Antihunting electrical measuring and control apparatus



June 14, 1949. T. R. HARRISON ETAL 23,121

I ANTIHUNTING ELECTRICAL MEASURING AND CONTRQL APPARATUS 5 Sheets-Sheet 1 Original Filed NOV. l5, 1958 FIG.

inn FIG. 2

FIG. 7

INVENTORS THOMAS R.

HARRISON WALTER R WILLS ATTORNEY R. HARRISON ETAL ANTIHUNTING ELECTRICAL MEASURING AND CONTROL APPARATUS June 14, 1949.

Original Fi led Nov. 15, 1958 5 Sheets-Sheet 2 FIG. 4

FIG. ll

FIG. l2

INVENTORS THOMAS R'HARRISON WALTER P. WILLS ATTORNEY June 14, 1949. 'r. R. HARRISON ET AL Re. 23,

ANTIHUNTING ELECTRICAL MEASURING AND CONTROL APPARATUS 5 Sheets-Sheet 3 Original Filed Nov. 15, 1958 INVENTORS THOMAS R. HARRiSON WALTER P. WILLS ATTORNEY 1 June 14, 1949. T. R. HARRISON ETAL' 23,121

ANTIHUNTING ELECTRICAL MEASURING AND CONTROL APPARATUS 5 Sheets-Sheet 4 Original Filed Nov. 15, 1938 June 14, 1949. T. R, HARRISON ET AL 23,121

ANTIHUNTING. ELECTRICAL MEASURING AND CONTROL APPARATUS Original Filed NOV. 15, 1958 Sheets-Sheet 5 FlG. I?

lu LT i402 Tl v Q {I} m I 7 I I65 I68 I69 nunnnuuonnuu R FIG. l9

4/ 1 INVENTORS L THOMAS R. HARRISON WALTER P. WILLS ATIORNEY Reissued June 14, 1949 UNITED STATES PATENT" OFFICE ANTIHUNTI I NG ELECTRICAL MEASURING AND CONTROL APPARATUS Thomas R. Harrison, Wyncote, and Walter P Wills, Philadelphia, Pa., assignors, by mesne assignments, to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corpora tion oi Delaware Original No. 2,300,742, dated November 3, 1942,

Serial No. 240,594, November 15, 1938. Application for reissue January 22, 1949, Serial No.

31 Claims. (Cl. 31828) The present invention relates to' a method of and apparatus for preventing hunting in automatic recording and control systems.

A general object of the invention is to provide 7 an effective method of and apparatus for regulating a condition such as. mechanical, electrical, chemical, physical, etc; in such a manner'as to prevent hunting.

A specific object of the invention is to provide stationaryi anti-hunting means for use in recording and/or controlling systems.

A further object of the invention is to provide a temperature recording and/or, controlling systern-that shall embody means for preventing hunting.

In accordance position of rebalance. when such a condition of overshooting prevails, the network then be-* comes unbalanced in the opposite direction and initiates operation of the driving'system to obtain rebalance but again the necessaryregulation' is exceeded to thereby set up a continuous hunting of the driving system about the balance r a with one embodimentof the invention, a self-balancing system including an electromotive force varying in accordance with the variation in magnitude of a condition under ing the electrical network on a variation in the condition under measurement that the inertia of the driving system is compensated for and hunting or oscillation of the said system about the balance point is prevented. The delaying means are of such character that the operation of the driving system is effective substantially immediately in effecting rebalance of the network whereby the operation of the driving system will be proportional to the extent of network unbalance; By providing such delaying means the full extent to which the network will be unforce is not immediately applied to produce operation of the driving system, but is applied thereto in accordance with the inertia of said system to thereby compensate for such inertia and prevent hunting of said system. Thus, the driving system will decelerate as the full unbalance of the point.

Theneedfor anti-huntingprovisions in re- I cording and controlling apparatus haslong been recognized andv various methods have been proposed for obtaining thesame. One 'such prior art method for "preventin hunting, is disclosed in Patent 1,827,520 issuedvto- Thomas R. Harrison on October 13, 1931, for Recording and control systems and apparatus therefor in which-the speed of rebalance of an electrical network is eilected in accordance [with the extent of 'unbalance thereof, and mechanically moving means are providedior maintaining proportionality between the extent oi unbalance and speed of re balance.

In the practical carrying'out of the present invention, for example, in controlling the tembalanced on a change in the said electromotive operate as to carry the driving system and associated rebalancing means beyond the proper perature of a furnace, we may employ a device such as a thermocouple as the means responsive to the temperature of the interior of the furnace, and. apply the thermal. electromotive force de- .veloped by the heat of the furnace through a resistance of suitable value to charge a condenser and measure the charge on the condenser to determine the temperature of the furnace. In one practical embodiment of our invention the electromotive force between the condenser terminals is compared to a standard or known electromotive force across a slidewire resistance having a contact adjustable along the length I thereof for tapping off any portion of the totalelectromotive force across the slidewire- A suitable detecting device is connected in circuit with the known and unknown electromotive forces and initiates the operation of a reversible motor having a mechanical connection to the slidewire contact and adapted to adjust the latter along the length of the slidewire to render the known and unknown electromotive forces equal and opposite. In the operation of the apparatus the electromotive force across the terminals of the condenser gradually builds up to a value equal to the thermal electromotive force and on a, change in the latter does not instantaneously follow such changes. As a result the full unbalance which will result between .the electromotive force developed by the thermocouple and that tapped on the slidewire resistance on a 3 given change in thermal electromotive force is not immediately applied to the detecting device but is gradually applied thereto. By properly proportioning the values of the condenser and the resistance through which th condenser is charged by the thermal E. M. F. to the resistance of the detecting device and the slidewire, the rate at which the network unbalance is applied to said detecting device may be adjusted as required to exactly compensate for the inertia of the detecting device, the driving motor and the mechanical connection to the slidewire contact. Thus, the speed'of the motor in effecting rebalance may be extremely high without overshooting of the balance point taking place.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects attained with its use, reference should be had to the accompanying ometric network includes a slidewire resistance drawings and descriptive matter in which we have illustrated and described a preferred embodiment of the invention.

Of the drawings; v

Fig. 1 is a diagrammatic representation of the use of the invention in a potentiometric recording system;

Fig. 2 illustrates in detail a form of interrupter that may be employed in the arrangement of Fig. 1;

Fig. 3 illustrates schematically a form of amplifier that may be employed in the Fig. 1 arrangement;

Fig. 4 illustrates a modification of the'Fig. 1 arrangement; 7

Figs. 5-7 illustrate in detail a form of interrupter that may be employed in the arrangement of Fig. 4;

Fig. 8 illustrates a further modification of the arrangement of Fig. 1; Figs. 9 and 10 illustrate in detail a form of interrupter that may be employedin the arrangement of Fig. 8;

Figs. 11-15 illustrate further modifications of the Fig. 1 arrangement;

Figs. 16-18 illustrate still further modifications of the arrangement of Fig. 1 and are diagrammatic representations of the use of the invention with electrical bridge networks; and

Fig. 19 is a diagrammatic representation of theuse of the invention in a control system.

Referring more particularly to Fig. 1 of the drawings there is illustrated in schematic form an arrangement including an electronic device I, shown in detail in Fig. 3, for producing effects in accordance with the extent of unbalance of a potentiometernetwork which controls the elec- 1 tronic device and is unbalanced in accordance with variations in a quantity to be measured, and in which because of the small magnitude of the unbalanced electromotive forces it is not practical nor desirable to have the said efiects produced directly by the potentiometric network.

More specifically, an arrangement is illustrated in Fig. 1 formeasuring and recording the temperature of a furnace (not shown) in the interior of which a thermocouple 2 is arranged in heat transfer relation therewith and is responsive to slight changes in temperature therein. The thermocouple, which may be located at a dis-Y tance from the remainder of the measuring apparatus, has it's terminals connected by a pair of conductors 3 and 4 to the terminals of a null.

point potentiometric network 5. The potenti- 8 and an associated contact I, which is capable of being moved along the length of the slidewire, and may be of any suitable type, for example,

such as the Brown potentiometric network discontact 1 along the slidewire resistance 5 to rebalance the potentiometer when the latter is unbalanced.

One terminal of the thermocuple 2 is connected by the conductor 4 directly to the left end of the slidewire resistance 8, as seen in Fig. 1, and the other terminal of the thermocouple is connected by the conductor 3, in which a resistance H is inserted, to one terminal I2 of an interrupter or converting device l3 described in detail hereinafter in connection with Fig. 2, and a second terminal I! of the interrupter is connected by a conductor 15, in which a resistance I6 is inserted, to the contact I. The function of the resistance II and an associated condenser I] which is connected from the end of resistance I l remote from the thermocouple to the left end of the slidewire resistance 6 is to prevent hunting of the system and will be explained in detail hereinafter.

The interrupter l3, illustrated schematically in Fig. 1 and in greater detail in Fig. 2, operates to convert the potentiometer unbalance direct currents into pulsating currents capable of being readilyamplified. It will be understood any desired form of interrupter may be employed, but in order to illustrate an operative form the interrupter shown in detail in Fig. 2 may be employed, said interrupter consisting of a vacuum tube It in which metal terminals or contacts l2 and ll are arranged. The tube I8 may desirably be formed of glass and has a diaphragm at one end which is resilient and integral with a rod I9 the latter of which has an end 20 normally resting against the underside of the contact I so that upon movement of the rod l9 downward, the contact 14 is raised out of engagement with the contact II to thereby break the circuit at that point. As soon as the rod I9 is moved upward, the contact M will move downward into engagement with the contact l2 to again close the circuit. The rod I9 is operatively connected by means of a link 2| to a vibrator 22 which may be of an electromagnetic type, as shown, and receives energizing current from alternating current supply lines L and L, which may desirably, .f'

although not necessarily, be a source of 60 cycl current.

On energization of the vibrator 22, t e contact M will alternately be raised and lower d thus intermittently breaking the circuitbetwen It is noted the vibrator may determinals of the electronic amplifier I wherein it is amplified and the amplified quantity is'aplied to the terminals of one winding II or 24 of the reversible motor- I l which, as illustrated, in detail in Fig. 3, also includes a winding 25 connected to the supply lines L andL through a suitable condenser 26.

The reversible motor ll is of the induction variety and includes a squirrel cage rotor and two pairs of oppositely disposed field poles on which the windings 23, 24 and are wound. Winding 23 is wound on one field pole of said pair, and winding 24 iswo'und-on the other pole of said pair. Winding 25 is wound on the other pairof field poles and due to the action of condenser Z G, the current whichfiows through the winding 25 willlead the line current by approximately 90. The current supplied the winding 13 by the amplifier i is in phase with the supply linevoltage and establishes a .fieldin the rotor which is displaced 90 in the forward direction with respect to that established therein by the winding 25. Similarly, the current supplied winding. 24 is in phase with the supply line voltage but since itis wound on an opposite field pole from that on which the winding 23 is wound,

winding 24 establishes a field in the rotor which lags by 90 that established by winding 25. Reaction between the field set up by winding 23 or 24 with that set up by winding 25 establishes a rotating field in the rotor which rotates in one direction or the other dependent upon whether shaft 9 so that the contact I is adjusted along the slidewire resistance 6 in accordance with the direction of rotation of the rotor. The direction and duration of rotation of the rotor is controlled by the direction and extent of unbalance or the potentiometer so that on motor rotation the con-,

potential across the Q tact 1 is adjusted in the proper direction to reduce the potentiometer unbalance.

In order that the speed of motor III may be as great as possible without overshooting of the new balance point of the potentiometric network 5 and consequent hunting taking place, means have been provided to insure that the motor speed is reduced to zero as the balance point is reached.-

This end is obtained by providing the arrangement including the resistor II and condenser IT, as shown.

With the resistance II and condenser Il connected as shown, it will be apparent the thermocouple 2 operates to charge the condenser I] through the resistance Li and the electromotive force thus developed between the condenser terminals is compared with the potentiometer electromotive force at the then position of the contact 1. The resistance l l is preferably of, such value that the total resistance of the circuit including the thermocouple 2, leads 3 and l and the resistance Ii is several times greater than that of the circuit including the potentiometer slidewire 6, resistance [6, and the interrupter contacts I2 and II when the latter are in engagement. -The operation of this arrangement for preventing hunting will 'now be described.

With the temperature of the furnace, to which the thermocouple is responsive. ata predetermined value, the condenser I! will tend to be charged through the resistance l l until the condenser electromotive force is equal to that oi the thermocouple. The contact 1 will then be in a position along the slidewire resistance 6 such that the electromotive iorce tapped oil the, slidewire 6 is exactly equal and opposite to the condenser electromotive force. For convenience, when the slidewire electromotive force is referred to hereinafter, that portion tapped of! resistance I and opposed to the condenser electromotive force is the electromotive force intended. On a change in the temperature of the furnace, for example, on an increase in temperature, the thermal electromotive force will increase and operate to charge the condenser I! further and thereby increase the electromotive force developed across the condenser terminals. The flow of current through resistance II will produce a potential drop across the latter and, as a result, the electromotive force developed across the condenser terminals will not assume the final value of the thermal electromotive force until the current through resistance II is reduced to zero, or in other words, until the system is again balanced, Thus, until the slidewire electromotive force is adjusted to the new value of thermocouple electromotive force, the electromotive force developed on the condenser will tend to assume a valueintermediate the thermocouple and slidewire electromotive forces. The flow of current through resistance 16 on unbalance of the condenser and potentiometer electromotive forces will operate substantially immediately to produce energization of motor 10 for rotation to effect adjustment of the contact I in the proper direction to reduce the unbalance between the condenser and potentiometer electromotive forces. Itv is noted that while the currents which flow through the resistance I B result primarily from changes in the thermocouple electromotive force, the magnitude of those currents is deterthermocouple electromotive force only in so far as the latter changes the condenser electromotive force.

It is noted there is no delay means in the circult through which the condenser and slidewire electromotive' forces are opposed so that the amplifier i'resppnds substantially immediately to unbalance in said electromotive forces to energize the motor ID for rotation in one direction or the other to change'the slidewire electromotive force as required to reduce the unbalance, and reduces the motor energization to zero at the instant the balance between the said electromotive forces is restored. Due to the inertia of the motor, however, the speed of the latter will not fall off as quickly as the energization thereof and consequently the slidewire electromotive force will overshoot the instantaneous value of the condenser electromotive force. As a result the potentiometric network will be momentarilyunbalanced in the opposite direction, which unbalance will produce an efi'ect energizing the motor for rotation in the reverse direc tion to thereby quickly decelerate the latter." Incan:

asmuch as the condenser electrom'otive force differs from the thermocouple electromotive force by an amount equal to the potential drop produced across resistance II by the flow of current therethrough, the contact 1 will not have reached connected to the other terminal of the winding.

the position'along slidewire resistance .0 corresponding to the new value of thermocouple electromotive force at-the instant when the condenser and slidewire electromotive forces were exactly balanced. It is noted that after the condenser and slidewire electromotive forces are balanced the condenser will not assume the thermocouple electromotive force until the lapse of a predetermined interval required to charge the condenser to the thermocouple potential, and by making this interval of the proper duration, the motor will be decelerated and ease the contact I gradually into said position without overshooting it. The proper adjustment of the duration of the lag between the condenser and thermocouple electromotive forces may be readily effected by properly proportioning resistance H and condenser ll in relation to the eflective resistance of the circuit including the contacts l2 and I4 and resistances 6 and I6. Thus, on a change in thermocouple electromotive force, the motor will effect an adjustment of the contact I along the slidewire resistance 6 and closely adjacent the balance position the motor speed will be quickly decelerated and said motor will come to rest with the contact 6 at the exact balance position. If, for any reason, the motor should stop short of the exact balance position, the condenser I! will be further charged to thereby .produce a torque actuating the motor for rotation in the proper direction, thereby insuring that the system will be adjusted to the exact balance position. It is noted the motor may be extremely fast in its rebalancing effect and is capable of moving the contact I completely along the length of the slidewire resistance, a distance approximately twelve inches, in some cases, in

a fraction of a second without overshooting taking place.

If desired, a pen may be mounted on the car riage 8 which carries the potentiometer contact I and arranged in cooperative relation with a recorder chart 21 to thereby provide a continuous record of the temperature of the furnace in which the thermocouple 2 is inserted. The chart 21 may be a strip chart, as shown, and is adapted to be driven in any convenient manner, as for example, by a unidirectional motor 28 through suitable gearing (not shown), so that a record of the temperature to which the thermocouple 2 is subjected will be recorded as a continuous line on the chart.

The electronic amplifier I referred to is illustrated in detail in Fig. 3 and, as shown, includes an electronic valve 29 which is preferably a heater type 'high mu triode having an anode, cathode, and a, control electrode, and having its input circuit connected by conductors Ill and 3|. to the terminals of the resistance l6. Anode voltage is supplied the valve 29 from the termi- V nals of a suitable filter 32 which is connected in circuit between the valve 29 and a rectifier 33. The rectifier 33 is a conventional full wave rectifier employing a rectifier valve 34 including two heater type diodes in one envelope. Energizing current is supplied the heater filaments of the diodes from the low voltage secondary winding 35 of a transformer 36 which also includes a line voltage primary winding -3'I, a high voltage secondary winding 38, and a second low voltaee' a 's secondary winding; The anode of one-diode of valve is connected to one, terminal of the winding M and they anode of the second diode is shunts its positive and negative terminals, and A has its positive terminal connected to the anode 'of valve 29 through resistances 42, 43 and 44,

and its negative terminal connected directly to the cathode of said valve. point of engagement of resistances 42 and 43 is connected by a condenser 45 to the negative terminal of the filter and the point of engagement of resistances 43 and 44 is connected by a condenser 45 thereto.

Energizing current is supplied the heater filament oi valve 29 from the low voltage transformer winding 39 which also supplies energizing current to the heater filaments of a twin type valve 41. The flow Of current through valve 29 is normally maintained at a mean value since the resistance It is connected directly across the input circuit thereof, but when a pulsatingpotential appears across the'terminals of resistance II, the conductivity of valve v29 is alternately increased and decreased resultin in a pulsating potential drop appearing across the resistance 44 in the output circuit of the valve 29.

The output circuit of valve 29 is resistance capacity coupled to the input circuit of valve 41 through a condenser 48 and a resistance 49 connected across the input circuit of valve 41. Valve 41, is a, heater type'valve including two triodes in one envelope. Each triode includes anode, cathode, and control electrode elements. For convenience, the triode having the resistance 43 connected across its input circuit will be referred to as the triode A and the second triode will be referred to as the triode B.

Anode voltage is supplied the triodes A and B from the terminals of the filter 32 and, as shown, the anode of triode A is connected through a resistance 50 to the point of engagement of resistance 42 and 43 and the anode of triode B is connected through the primary winding 5| of a transformer 52 to the positive terminal of the filter. The cathodes of triodes A and'B are connected together and to the negative terminal of the filter.

The output circuit of triode A is resistance capacity coupled by a condenser 54 and a resistance 55 to the input circuit of triode B, and the output circuit of the latter is coupled by transformer 52 to the input circuit of a pair of electronic valves 55 and 51 connected in push-pull.

is connected through a biasing resistance to the cathodes of the valves, which, as shown, are connected together. As illustrated, a. condenser 58 may desirably be connected across the terminals of the transformer secondarywinding 53 for tuningthe latter to the frequency it is desired to amplify. Valves 56 and 51 are heater type tetrodes and include anode, cathode, heating filament, control electrode, and screen elements.

As illustrated, the

Anode voltage may be supplied the valves 55 and 51 directly from'the supply conductors L and L as shown, or may be supplied thereto from a suitable transformer energized by the supply line current, if desired. Winding 23 of motor III is connected in the anode circuit of valve 58 and winding 24 of the motor is connected in the anode circuit of the valve 51. In operation, when a pulsating potential drop is produced across resistance II as a result of potentiometer unbalance, the resulting amplified pulsating current flows through the transformer primary winding will cause the induction of an alternating voltage across the terminals of the transformer secondary winding 53, which voltage is impressed on the input circuits of valves 56 and 51. The alternating voltage which appears across the terminals of the transmormer winding 53 swings the potentials of the control electrodes of the valves 56 and 51 in opposite phase at a frequency corof valves 56 and 51 to increase the available torque of motor In.

In Fig. 4 we have illustrated, more or less diagrammatically, a modified form of our invention embodied in a self-balancing potentiometer recording system of the general type described in connection with Fig. 1. In this modified arrangement the potentiometric network 5 and the input circuit of the amplifier I, which amplifer may be identical with the correspondingly identified part of Fig. 1 and described-in detail in Fig. 3, are coupled by a transformer Ilia having a center tapped primary winding lib and a secondary winding lie, and a double contact interrupter l3a is employed for chopping the unbalance potentiometer currents to permit easy amplification thereof. A modified anti-hunting circuit connection is provided in this arrangement, which modified circuit includes a resistance lid inserted in the thermocouple lead 3 and a condenser Ila which, as indicated, is connected across the said resistance. The operation of this anti-hunt- .ing arrangement will be explained further hereinafter.

As illustrated in Fig. 4 and in greater detail in Figs. 5-7, the interrupter 13a includes an arm or flexible reed I31 which is adapted to be vibrated and is preferably in engagement with a pair of contacts. I So and l3d when in a. mid-position but disengages one contact when moved in one direction and disengages the other contact when moved in the opposite direction. The contact l3c is connected to oneterminal of the primary winding 3b of transformer lGa and the contact l3d is connected to the other terminal of the winding. The reed [If is vibrated at a frequencyidentical with that of the supply lines L and L and operates to cause the flow of unbalance'potentiometer currents alternately through the opposite halves of the transformer primary winding lib to thereby cause the induction of a voltage in the transformer secondary winding l6c, which voltdirection.

age is in phase, or displaced in phase, with the supply line voltage depending upon the direction of potentiometer unbalance. The voltage so induced in the winding llic is amplified by the amplifier land the amplified quantity is employed to cause the selective energization of motor III for rotation in one direction or the other and thereby adjustment of the contact I in the proper direction along the slidewire resistance 6 to rebalance the potentiometer. It is noted that by employing the double contact interrupter and the center tapped primary winding l6b stray E. M. F.s of the same frequency as the line frequency which may be induced in the thermocouple leads or potentiometer slidewire resistance 6 are cancelled out in the transformer lfia. This feature is desirable in practical embodiment of systems utilizing our present invention.

The operation of the anti-hunting means provided is this arrangement will now be explained. In operation, when the potentiometer is balanced, the current flow through resistance Ila will be zero and consequently there will be no charge on condenser Ila. One. change in thermocouple E. M. F., however, resulting in potentiometer unbalance, the flow of unbalance potentiometer current will begin charging the condenser I'm to develop an electromotive force across the condenser terminals-which thereafter will be discharged through resistance I la.

It is noted that'at the instant the thermocouple voltage begins to change, the condenser l'la will have no effect on the system but as soon as the unbalance currents begin to charge the condenser an electromotive force is gradually built up on the condenser which electromotive force reduces the flow of unbalance currents and thereby produces delay in the application of the full change in the thermoelectric voltage on the potentiometric network. Specifically, the condenser will be charged by the flow of unbalance currents and the polarity of the charge will be in opposition to the unbalance electromotive force to thereby reduce the portion of the unbalance electromotive force to which the amplifier l is responsive. Thus, as in the arrangement of Fig. 1, the motor energization will fall off as the unbalanced potentiometric electromotive force is reduced and will coast beyond the position at which its energization is entirely cut oil to thereby unbalance the potentiometer in the opposite The motor will then be energized for rotation in the opposite direction and quickly come to rest with the contact I at the exact balance point. By properly proportioning the resistance H and condenser ila to the effective resistance of the vibrator contacts, winding lSb,

I and resistance 6, the amount by which the condenser reduces the application of the full change in thermocouple electromotive force to the amplifier I may be made precisely that required to prevent overshooting of the balance point by the motor.

It is noted that while the anti-hunting arrangement of Fig. 4 differs somewhat in structure from that disclosed in Fig. 1 they both have in common extreme simplicity and ability to prevent hunting of a mechanical rebalancing action without requiring the use of physically movable devices. It will be understood that the antihunting arrangement of Fig. 4 may be employed with equal facility in the system of Fig. 1 and vice versa;

The mechanical construction of a preferred form of interrupter is illustrated in detail in 11 Figs. -7 wherein it will be seen the interrupter includes a U-shaped permanent magnet 13c, a deflecting member or reed l3! shown more in detail in Fig. '7 and an actuating coil l3g. Coil l3g has its terminals connected to the altermating current supply conductors L and L through a suitable transformer (not shown) and is rigidly supported by two U-shaped soft iron members I371. and In the latter of which are attached by screw means to the inner surface of a respective pole of magnet lie. i3h and I31 are arranged with their legs facin each other and separated bya distance sufficient to permit a small movement of the deflecting element I3f, which element, as shown, is positioned between said legs and also extends through the center portion of coil Hg.

The members As shown in Fig. '7, the deflecting element I31 1 comprises a flexible metallic reed having a slit at one end which extends for a portion of the length of the reed to divide that end of the latter into two legs each of which carries an electrical contact, one of the contacts being arranged on the upper side of the reed and the other contact being arranged on the lower side as seen in the drawings. The reed I3) is carried by a rectangu lar metallic plate I37 and is rigidly secured thereto as for example by soldering or welding, being so arranged with respect to the plate that one half of the reed extends at right angles from one side of the plate and the other half of the reed extends at right angles from the other side of said plate. As illustrated, slits somewhat longer than the width of reed lflf are provided in the plate I 31' above and below the said reed so that when the plate is held stationary, the reed may be deflected relatively to the plate, and if deflected and suddenly released, will vibrate.

As illustrated in Fig. 5, the plate 137' is supported by the lower legs of members 13h and Hi and is held tightly against said legs by a Bakelite block l3k, which in turn is attached by screw meifns passing through the said block and the plate Bi and threaded into the legs of members 13h and I31. Block I310 is provided with an oval opening into which the slitted end of reed I3f extends, and also carries the contacts I and l3d which are normally in engagement with a respective contact carried by that end of reed l3f. On deflection of the reed l3f, however, the slitted end thereof will bend slightly to thereby break the contact at a contact I30 or l3d according to the direction of deflection. Thus, when the reed is vibrated, the contact at 13c and i311 will periodically and alternately be opened toeffect the desired action described hereinbefore.

Such vibration of reed I3) is produced in a manner to be described when coil l3g is energized by alternating current. When coil llg is so energized the upper half of reed l3 will become magnetized in opposite directions at the supply line frequency, and reaction of the magnet so produced with the poles of magnet He will operate 'to deflect the reed first in one direction and then in the opposite direction at the supply line frequency to thereby cause an opening action at each of the opening contacts I30 and 13d once in each cycle of said frequency. It is noted that the lower legs of members Ian and I31 do not aid in producing vibration of reed i3f, but may desirably be provided to shield the lower end of said reed from stray lines of magnetic flux to prevent the induction therein of E. M. F.s which will operate to introduce inaccuracy'into the measurement. In order to obtain the maximum 12 effect therefore, the ends of 'the lower legs to members Iih and Iii may desirably be closer together than the ends of the upper legs.

In. Fig. 8 we have illustrated schematically a further modification of the arrangement of Fig. l'wherein a double contact interrupter I3A- is employed which operates to apply the thermocouple E. M. F. to the condenser I! when in one position and to oppose the E. M. F. so developed on the condenser through conductors 58 and 59 and resistance It to the potentiometer E. M. F. when in an opposite position. The interrupter ISA is described in detail hereinafter in connection with Figs. 9 and 10 and when in the position last mentioned above isolates the thermocouple 2 and resistance II from the remainder of the network. The operation of this arrangement for eliminatingany tendency of the system to hunt is the same as that of the Fig. 1 arrangement and hence further explanation is not believed necessary.

As illustrated in Figs. 9 and 10 the interrupter ISA includes a continuously rotating shaft I3B which may be driven by any suitable form of motor such as a synchronous motor HA and on which shaft are insulatingly mounted two pairs of slip rings I30, RD and BE, [3F and a four segment commutator IIG, each se ment being of the same arcuate length and all insulated from each other. Brushes I3H and I31 are provided for the commutator I3G and corresponding brushes "J, K, ISL, IBM are provided for the slip rings I36, i3D, [3E and HF, respectively. The brushes ISH and I3! are connected to conductors 50 and 59 respectively,

,while the brushes IIJ and ISK are connected to conductors 3 and l, in the former of which the resistance II is inserted. and the brushes 13L and I3M are connected to one end terminal of slidewire resistance 6 and to contact I respectively. One opposite pair of segments on the commutator I3G are connected to the slip rings I 3C and IBD and the other opposite pair of segments are connected tothe'slip rings 13E and HF. Thus, during each cycle of rotation of the shaft i3B, one pair of segments on the commutator will be in engagement with the brushes I3H and I3I for a half cycle and during that time close the circuit from the thermocouple leads 3 and 4 to the conductors 58 and 59, and during the remaining half cycle the other pair of commutator segments will be in engagement with the said brushes to connect the potentiometer slidewire G in circuit with the leads 58 and 59. The speed of the motor HA which drives shaft I3B, is so adjusted that the time for one cycle of rotation of the shaft is identical with the time of one cycle of the alternating current supply lines L and L In Fig. 11 we have illustrated a modification of the Fig. 8 arrangement wherein the thermocouple 2 is isolated from the' potentiometric network 5 and the amplifier l at all times. an arrangement is desirable when there is leakage between the thermocouple and ground, either resistance or capacitance or both. Referring to Fig. 3 it will be noted the cathode of the input valve 29 of amplifier I is connected directly to ground so that if such a leakage path exists, a closed. circuit will be established in which will flow stray currents which may be induced in the thermocouple leads, or established due to electrolytic action between the thermocouple and ground to introduce inaccuracy into the measurement. The operation of this ar- Such 13 rangement for eliminating any tendency of the system to hunt is the same as that of the Fig. 1 arrangement and, hence, further explanation is not believed necessary.

In this modified arrangement the resistance It and conductor 59 are permanently connected to the potentiometer slidewire resistance 8 and the interrupter 13A operates to alternately connect the condenser I! to the thermocoupl leads 3 and 4 and to the conductors 5B and 5!. As will become apparent, when the condenser electromotive force is identical to that tapped off the potentiometer slidewire resistance by the contact 7, no currents will flow in the potentiometer circuit, but when an inequality exists between the said electromotive .forces, a pulse of current will now through resistance l6 during one half of eachhalf cycle of rotation of the interrupter shaft I3B, the direction of flow of said pulse of current depending upon the direction of potentiometer unbalance. The pulsating potential drop so produced across resistance I6 is amplified by amplifier i and operates in the manner described in connection with Fig. 1 to cause the selective energization of motor "I for rotation in one direction or the other.

It is noted that the effects of stray currents in the thermocouple leads can be minimized by employing transformer coupling between the potentiometer and the amplifier as illustrated in Figs. 4 and 7 but the flow of suchpcurrents is not entirely eliminated by means of such an arrangement because of the capacitative coupling which exists between the-primary and secondary windings of the coupling. transformer [60. With the arrangement illustrated in Fig. 11 the flow of such stray currents is entirely prevented so that resistance coupling may be employed between the potentiometric network and the amplifier-in lieu of the relative costly transformer coupling thereby effecting a material reduction in the apparatus involved.

Referring to all of the previous arrangements described and particularly to Fig. 1, it is noted that if the sum of the resistance of the thermocouple 2 and the leads 3 and I is high, for example, of the order of the value of resistance II, the latter may be dispensed with and precisely the same anti-hunting effect obtained. As illustrated, in Fig. 12 for example, a photocell 2a may be employed in lieu of the thermocouple v2 as the condition responsive device, and since a photocell permits the use of high resistance circuits, it is not necessary to employ a resistance corresponding to the resistance H in this arrangement in order to prevent hunting of the system. The photocell may be focussed by means (not shown) on a source of light the intensity of which is tobe measured, and, as shown, it receives energizing current from a. battery 2b through a resistance which may be of a suitably high value.

- With the light intensity to which the photocell is responsive at a predetermined value, a direct current potential drop of predetermined value will be produced across the resistance 2c by the flow of photocell current therethrough and a condenser lld connected across the terminals of the resistance will tend tobe charged until the potential 'across the condenser is equal to that across the resistance 2c. The potential so developed across the terminals of the condenser lid isopposed through'a circuit; which circuit may be identical to that of theFig. 1 arrangement and including an interrupter It, to the pother description.

electromotive force tapped off the slidewire resistance is equal and opposite to the condenser electromotive force.

On a change in light intensity, for example, on an increase in intensity, the conductivity of the photocell will increase and thereby produce an increase in the potential drop across resistance 2c, which increase in potential drop will operate to charge the condenser lld further. The resulting unbalance between the slidewire and condenser electromotive forces will cause an unbalance potentiometer current to flow in resistance it which current is pulsating due to the action of interrupter l3 and is readily amplified by the amplifier I to selectively control the rotation of motor I and thereby the adjustment of contact I in the proper direction to reduce the unbalance potentiometer currents to zero. It is noted the flow of unbalance potentiometer ,currents through the resistance 20 willproduce a potential drop in the latter in opposition to that produced therein by the photocell current to thereby reduce the effective potential drop across the resistance 2c. Thus, as long as unbalance potentiometer currents flow in the circuit, the electromotive force developed across the condenser terminals will not assume the final value of electromotive force as produced in the resistance 2c by the flow of photocell current. The operation of this arrangement in producing an anti-hunting effect will thus be seen to be identical to that of the previous arrangements described in that the motor it! will be energized for rotation until the slidewire and condenser voltages are exactly equalized, at which point the motor energization will be cut off, The coasting of the motor due to inertia will thereafter produce a further change in the slidewire electromotive force to cause the latter to overshoot the instantaneous value of condenser electromotive force. As a result the potentiometer will be unbalanced in the opposite direction and produce an effect energizing the motor for rotation in the opposite direction to thereby quickly decelerate the motor. When the difference'between the potential drop produced across the resistance 2c by the flow of photocell current and the potential produced across the, condenser has been properly proportioned, the motor will then come to rest in a minimum of time with the contact 1 at the exact balance position along theslidewire resistance 6 then corresponding to the value of light intensity to which the photocell 2a is subjected.

In Figs. 13 and 14 we have illustrated further modifications of the Fig. 1 arrangement which embody our invention, and wherein unbalance of the potentiometricnetwork 5 is detected by a suitable galvanometer having a movable coil I on which the unbalance potentiometer currents' are impressed, and which deflects in one direction or the other depending upon the direction of potentiometer unbalance. The damping provisions employed in Fig. 4 are identical with those disclosed in Fig. 1 and hence need no fur- Any suitablemeans may be employed to detec the movement of the galvanometer coil II for producing a potentiometer rebalancing effect, as

for example, mounting a switch arm on the eter.

tioned pole.

. 15 galvanometer coil, which switch arm will engage one contact or the other of a relatively stationary reversing switch when the said switch arm de-.

fiects from a position between the contacts, but we prefer to use the arrangement illustrated which comprises a mirror 62 carried by the galv vanometer coil Iii, a relatively stationary source oi light or lamp 63, a pair of photocells GI and I! connected to the terminals of an electronic amplifier 66 which may be of any suitable type and a lens 62a for focusing the reflected beam of .light from the mirror 62 on the photocells.

, photocells is amplified bythe amplifier 6i and the latter operates when one photocell receives more light than the other to selectively control the energlzation of a reversible motor Illa for rotation in one direction or the other and thereby the rebalancing operation of the potentiombut as illustrated, is somewhat different in that half of winding 23 is wound on one field pole and the other half is wound on an oppositely disposed field pole. Similarly, half of winding 2| is wound on the first mentioned field pole and the other half is mounted on the second men- In Fig. 14, an arrangement is illustrated wherein the rebalancing motor is not directly connected to the electronic amplifier but is controlled for rotation by apair of relatively slow acting relays selectively energized by the amplifier. In this embodiment anti-hunting means are providedwhich are of especial utility when the motor is energized by slow acting relays. As described in further. detail hereinafter, the anti-hunting means are not effective immediately on theoccurrence of potentiometer unbalance to cause a delay in the application of the change in thermocouple electromotive force to the potentio-, metric network, but are effective to cause such a delay when a motor energizing circuit is closed by one of the relays. In other respects the antihunting provisions of this embodiment are identical in operation to that of the Fig. I arrangement.

As illustrated, the photocells 64 and B are connected to the input circuit of an electronic amplifier 68' having a pair of coils 83 and 84 connected in the output circuit thereof. The amplifier 66 may be of any suitable type and may be similar to the amplifier 65, if desired, except that suitable provisions are made for connecting coils 83 and 84 in the output circuit instead of the motor windings 23 and 24. The coil 83 is operatively associated with a pair of switch arms 85 and 89, which switch arms are normally in engagement with a respective contact and 00 but are adapted to be moved out of engagement therewith when the coil 83 is energized. The coil M is similarly operatively associated with'a pair of switch arms 81 and BI which normally are in engagement with a respective contact l8 and 92,,but are adapted to be moved out of engagement therewith when the coil 84 is energized.

The switch arms 89 and M are connected to- Motor Illa may be exactly like motor I0,

. gather and to the supply line L and the contacts 90 and I! are connected through a respective winding '93 and M of a motor lilb to the supply line L. Motor llb is a reversible type induction motor and rotates in one direction when the current fiow through the winding 93 leads that through the winding 84 and rotates in the oppo site direction when the current flow through the winding SI leads that through the winding 93. The desired shift in phase of the motor currents to produce rotation thereof is produced by means of a condenser 95 connected across the contacts SI! and 52. As noted, both switch arms 89 and II are normally in engagement with the contacts 90 and 92 so that motor lob is then energized for rotation in both directions and remains- .stationary. When one arm 89 or 9| is moved out of engagement with its associatedcontact, 'however, motor llb rotates in a corresponding direction.

The switch arms 85 and B1 and their associated contacts 88 and 88 are connected in a series circuit including a conductor 96 connected to one terminal of the resistance II and a conductor 81 connected to a contact Me which is adjustable along the resistance II.- The switch arms 85 and 81 .are both normally in engagement with their associated contacts and thereby close a low resistance shunt circuit about the resistance II to thereby render the latter ineffective to produce its anti-hunting efiect, but on energization of relay coil 83 or 84, the said shunt circuit is opened and the resistance II is rendered effective to prevent hunting of the system. With this modified arrangement, therefore, the full thermocouple electromotive force will be applied in controlling the operation of the motor lflb at the instant of the occurrence 01 a change in electromotive force of thermocouple 2, but as soon as the motor is energized for rotation, the anti-hunting means II and II will be rendered effective to prevent hunting oi the motor.

In Fig. 15 we have shown, more or less diagrammaticallya modification of the Fig. 12 arrangement illustrating the use of our invention in a self balancing measuring instrument employing a photocell as the condition responsive element. Specifically, the instrument illustrated comprises a photoelectric pyrometer of the general type disclosed in a copending application of Thomas R. Harrison, Serial No. 145,637, filed May 29, 1937, issued into Patent 2,245,034 on June 10. 1941. in which a photocell 9B is arranged to receive light from the interior of a furnace or from an incandescent body 99, and a second photocell Ill is arranged to receive light from a lamp ill, theillumination of which is adapted to be controlled by means responsive to the relative conductivities of the two photocells. The photocells are arranged in an electrical bridge circuit and as thetemperature ofv the incandescent body varies, the illumination of lamp IN is varied until the illumination of the two photocells is balanced. The magnitude of the lamp energizing current will be a measure of the condition and is measured by a sell! balancing potentiometric network to be described.

As shown,the two photocells are connected in series relation by a conductor I02 and the series arrangement is connected across a suitable portion of a voltage dividerllli by meansof conductors Ill and lli. The photocell 98 is preferably enclosed in a suitable casing (not shown), and the casing is arranged in such manner that the only light which impinges on the cell is that can! voltage primary winding II, low voltage secondary windings I00, I09. H0, and III and high voltage secondary windings H2 and H8. The low voltage secondary winding I00 is connected by conductors, not shown, to the heater filament of an electronic valve III, and suppiies energizing current thereto. Electronic valve Ill is a heater type triode and includes anode, cathode, filament, and control electrode elements and, as shown, the anode thereof is connected to one terminal of the voltage divider I03 by means of a conductor Iii in which a resistance H6 is inserted, the cathode is connected to a point on the voltage divider intermediate the points of connection of the conductors I04 and I00 thereto, and the control electrode is connected to the conductor I02 between the two photocells.

The low voltage secondary winding I00 is connected by conductors, not shown, to the heater filament or cathode of a second electronic valve I II and supplies energizing current thereto. The valve II! is a filament type triode and includes anode, cathode, and control electrode elements. The anode is connected by a conductor I It to the positive terminal of a second voltage divider Ill which voltage divider is energized from the transformer I00 in a manner to be described. As shown, the negative'terminal oi the divider II! is connected to the anode of valve I I4. A center point on the filament cathode of valve H1 is connected to a point on me voltage divider II! which is negative with respect to the point of connection of the anode thereto and has connected in circuit therewith the filament of lamp IOI anda resistance I20. The lamp IOI is thus arranged to be energized by the flow of current through valve Ill. The control electrode of valve H1 is connected to the positive terminal of the voltage divider I 03 so that as the flow of current through valve Ill varies to vary the potential drop across resistance Hi, the potential of the control electrode of valve III will change with respect to the filament cathode and the supply of current to lamp IOI will vary accordingly.

Electronic valves I2I and I22 are also provided, which valves may conveniently be full wave rectifiers and are employed to maintain direct current potentials across the voltage dividers I03 and H9, respectively. The filament cathode of upon, the control electrode 0! valve III becomes 18 are connected to the terminals oi the voltage divider I In so that a steady direct current voltage is maintained across the terminals of the divider.

When light from the incandescent body 90 is focussed on the photocell 00, the latter becomes more conductive and renders the control electrade of valve III more positive relative to the cathode thereof whereby the current conducted by the valve increases to produce an increase in the potential drop across resistance IIG. Theremore positive relative to its associated cathode resulting in an increase in the current conducted by valve III and thereby through the lamp IOI. As lamp IOI subsequently brightens, the photocell I00 becomes more conductive and drives the control electrode of valve III less positive, and since the latter controls the potential of the control electrode of valve 1, the conductivity of the latter is reduced. This establishes a balanced condition of the illumination of the two photocelis, and the energy used by lamp IN is then an indication oi the light being received by the photocell 00.

As previously noted, the current which passes through the lamp III! also passes through resistance I20 so that a potential drop is maintained across the latter which varies in accordance with the illumination received by the photocell 98 and thereby in accordance with the temperature or the incandescent body 09. This potential drop is opposed to and normally balanced by a measured part of the potential drop maintained across a slidewire resistance I25 by a voltage compensating bridge I28, which bridge operates to maintain the potential drop across resistance I20 constant irrespective of variations in line voltage over a substantial range. The voltage compensating bridge I2 is disclosed in a copending application of Thomas R. Harrison,

Serial No. 193,259 filed March 1, 1938, issued into Patent 2,211,114 on August 13, 1940, and includes resistances I21, I20, and I20 in three or its arms and a voltage regulator tube I30 in its remaining arm. Bridge I28 is energized from a suitable direct current source through conductors I3I and valve I2I is connected to and receives energizing current from the low voltage secondary winding H0, and the anodes thereof are connected to opposite terminals of the high voltage secondary winding II2. A center tap on the winding IIO and a center tap on the winding II2 are connected to the input terminals of a suitable filter I23 and the output terminals of the latter are connected to the terminals of the voltage divider I03 so that a steady direct current voltage is maintained across the terminals of the divider.

Similarly, the filament cathode of valve I22 is connected to and receives energizingcurrent from the low voltage winding III and the anodes thereof are connected to opposite terminals of the high voltage winding II3. A center tap on the winding III and a center tap on the winding II! are connected to the input terminals of a filter I20 and the. output terminals of the latter I32 which are connected to one pair of conjugate points, and the other pair oi conjugate points, one of which is the point of engagement of a contact I" with resistance I20, are connected to the terminals of the slidewire resistance I25. It is noted variations in the degree of compensatbn obtained may be efl'ected by adjustment of contact I33 .along resistance I20 so that on change in line voltage, the change may be exactly compensated or over compensated or under compensated, as desired.

Th source from which the bridge I20 is energized may be any suitable direct current source and, as illustrated, it may be energized through a suitable rectifier circuit from a transformer I34 which is a combination step-up and step-down transformer having a primary winding I35 connected to a source of alternating current, a high voltage secondary winding Ill, and a low voltage secondary winding Ill. The rectifier circuit referred to may be similar to the rectifier circuits including the valves III and I22 and includes a rectifier valve I" having its filament cathode connected to the terminals of the winding Ill and receiving energizing current therefrom. The anodes of valve Ill are connected to opposite terminals of the winding I30. The conductor I II is connected to a center tap on the ism " I32 for filtering the output current of the rectifier.

As illustrated, a resistance He and a resistance I are connected in a series circuit with the resistances I and I so that when the potential drops across the latter are not balanced, the currents which flow as a result of such inequality will flow through resistances He and Ill. The terminals of resistance 0 are connected by conductors MM and H012 to the input terminals of an electronic amplifier Ill which amplifier operates to amplify any potential drops produced across resistance Il0 as a result or the flow or unbalance currents therethrough and is adapted to selectively control the rotation and direction of rotation of a motor I0a in accordance with the polarity of the potential drop produced across resistance ll0. nected to a contact I25a, whichcontact is adjustable along resistance I25 for varying the magnitude of the slidewire potential inopposition to the potential across resistance I20 so that on a change in the illumination of photocell 00 and thereby in the current fiow through resistance I20, the contact I25a will be adjusted to a position along slldewire I25 which position corresponds to the new value of current through resistance I20.

The electronic amplifier I referred to includes a pair of electronic valves H2 and Ill,

Motor I0a is mechanically conwhich valves are heater type triodes including anode, cathode, filament and control electrode elements, and the output circuits of which are directly coupled to the input terminals of a like pair of valves Ill and H5. Valves Ill and N5, in turn, have their output circuits directly coupled to the input terminals of a pair of electronic valves M8 and M1, the latter of which are heater type tetrodes including anode, cathode, filament, screen and control electrode elements, and have a respective motor winding 20 and 2l connected in their output circuits.

Anode'voltage is supplied the amplifier from the high voltage secondary winding m of a transformer Ill], and, as illustrated, valves Ill and 5 are connected across the terminals of said secondary winding in an inverse manner with respect to the connection oi valves 2 and Ill' and valves Ilt and Ill thereacross. That is to say, valves Il2, I43, Ill and Ill and valves Ill and H5 will be conductive only during alternate half cycles of the supply line voltage so that the conductivities of valves Ill and 5 will be controlled in accordance with the magnitude of current conducted by valves M2 and M3 during the preceding half cycle and in like manner the conductivities of valves Ill; and I" will be controlled in accordance with the current conducted by valves Ill and M5 during the preceding half cycle. As illustrated, condensers I50, |5I and I52 are provided for each pair of valves, being connected between the anodes of a respective pair of valves, for eii'ecting such control of a successive pair of valves during the next later half cycle.

Transformer M9 is a combination step-up'and step-down transformerand includes a line voltage primary winding I53, the high voltage secondary winding I48, and low voltage secondary windings I54 and I5la. The low voltage wind-'- ing I5l supplies energizing current to the heating filaments of valves Il2, Ill; H5 and Ill and similarly winding I5la supplies energizing current to the heating filaments of valves Ill and Ill, each of the filaments desirably being corinected in parallel across its respective energizing winding. It is noted separate filament energizing windings I and I5la are provided since the potentials of the cathodes of valves Il2, Ill, H0 and I" are widely displaced from that of the cathodes oi! valves Ill and Il5.

Means are provided in this embodiment of our invention, as in the previousembodiments described, for preventing overshooting of the balance point and consequent hunting of the system, said means including the resistance IIe referred to and a condenser Ile connected between the terminal of resistance I Id remote from resistance I20 and the positive terminal of. the latter. This anti-hunting arrangement operates in a manner identical to that of the Fig. 1 arrangement and hence it is believed further description is not necessary. It is noted the potentiometer unbalanced currents involved are much greater than those encountered in amplifying thermocouple E. M. F.s but the principle of operation is the same.

It will be apparent the anti-hunting arrangement of our invention is not limited in its use to potentiometric networks, but that it may be employed with equal facility to other types of electrical networks, for example, with a Wheatstone bridge network, as illustrated more or less diagrammatically in Figs. 16-18. Specifically, an arrangement is illustrated in Fig. 16 for measuring and recording on a chart (not shown) the temperature of a furnace (not shown) to which temperature a device I56 is responsive, saidde- .vice being illustrated as a coil of material having a substantial temperature coefficient of resistance and connected in one arm of a Wheatstone bridge network I51. It is noted the resistance of the device I56 may be varied in waysother than in response to temperature changes, for example, 7

- other pair of bridge conjugate points are connected by conductors 3a and la, in the former 0! which a resistance Hg is inserted,- to the terminals of a galvanometer coil I, which coil may be identical to the correspondingly. identified part of Fig. 4 and the deflection of which selectively controls the direction of rotation of a motor l0a by means of a photocell and amplifier arrange: ment, as in Fig. 4. The remaining arms of the bridge network I51 are comprised of resistances I60 and IIiI, variable portions of the latter of which are adapted to be inserted into and taken out of two adjacent arms as a contact I62 in engagement with resistance IIiI and connected to conductor la' is moved along the length thereof. Contact I6! is mechanically connected to motor 1 IM so that as the latter is energized for rotation as a result of galvanometer deflection, contact I62 will be adjusted to a new balance position to reduce the bridge unbalance which initially caused the galvanometer deflection.

The means provided for preventing overshooting of the balance point and consequent hunting of the system comprise the resistance IIg-and a condenser IIy the latter of which is connected across the bridge arm I60 and the resistance IIg. In operation, on a change in the magnitude of the variable resistance I56 and a consequent change in the potential drop thereacross. a corresponding change in potential will immediately be effected across the resistance I60 due to the resulting change in current therein, but due to the action of the resistance lIg the potential across the terminals of condenser I'Ig will lag behind the potential across resistance I60. As the potential across the condenser terminals changes, the flow of unbalance currents through tact I62 is sufliciently fast so that before the con- .denser I1} has assumed its final value of electroeludes anode, cathode, and control electrodes. Energizing voltage is supplied the valves I63 and I64 from the high voltage secondary winding I66 of a transformer I66 having a line voltage primary winding I61 and two low voltage secondary windings I66 and I69. As illustrated, the left end terminal of winding I66 is connected by a. conductor I10 to the anodes of valves I63 and I64 which anodes are connected together, and the right end terminal of the winding is connected by a conductor I" to the negative terminals of a pair of biasing resistances I12 and I13. The resistances I12 and I13 are connected in a respective cathode circuit of valves I63 and I64. Energizing voltage is also supplied the bridge network I51 from the transformer secondary winding I65 and, as shown, the energizing terminals of the bridge network are connected by conductors I 14 and I15 to intermediate points at suitably motive force, the unbalance currents will be substantlally reduced to zero and even reversed in direction and therefore the energization of motor Ila reduced and reversed in direction before the true balance position of the contact I62 has been reached. The inertia of the motor will then carry the contact I62 to the exact balance position wherein it will come to rest.

It is noted that if the values of-res istances I56 and I60 are sufliciently high with respect to the remaining bridge resistances, the resistance Ilg may be dispensed with and the condenser I1g may be connected directly across the terminals of resistance I60, as illustrated in Fig. 17 and the same anti-hunting effect obtained.

In Fig. 17, we have illustrated a modification of the arrangement of Fig. 16 in which the bridge unbalance electromotive forces are. impressed by conductors Ia and H01) directly on the input terminals of an electronic amplifier MI in lieu of employing a galvanometer to detect bridge unbalance as in the Fig. 15 arrangement. The am- -01 condenser I1g the motor will be quickly decelerated as the balance position is reached and come to rest at the exact balance position without overshooting taking place. It is noted that the bridge unbalance currents may be interrupted by means of an interrupter I3 as in the Fig. 1 arrangement and an amplifier I employed to detect bridge unbalance if desired.

In Fig. '18 we have illustrated the use of our invention with a Wheatstone bridge network in which the unbalanced electromotive force in the network is first amplified and the amplified quantity is then passed through the anti-hunting network of our invention to control the rotation and direction of rotation of a motor I0a. adapted to- 3a and 4a to the control electrode of a respective electronic valve I63 and I64 each of which in-' different potentials on the winding.

When the bridge network is balanced the conductivities of valves I63 and I64 will be substantially identical and potential drops of equal mag nitude will be produced across the resistances I12 and I13. These potential drops are applied to the input circuit of a second set of valves I44 and I45 and the output circuits of the latter are coupled to the input circuits of a third set of valves I46 and I41. The valves I44-I41 and the coupling circuits therefor may be identical to the corresponding identified parts of Fig. 15. Energizing voltage is supplied the filamentsv of valves I44, I45, I63 and I64 from the transformer secondary winding I66 and energizing voltage is supplied the filaments of valves I46 and I41 from the winding I69. Anode voltage is also supplied the valves I44-I41 from the secondary winding I65. The valves I46 and I41, however, are connected to the winding in an inverse manner in respect to the connection of valves I44, I45, I63 and I 64 thereacross.

On unbalance of the bridge network the relative conductivity of the valves I63, and I64 will be varied to thereby produce potential drops of different magnitude across the resistances I12 and I13 in the cathode circuits of the valves. This difference in potential drops operates to control the conductivities of valves I44-I41 and thereby the selective energization of motor I0a for rotation in the proper direction to reduce the bridge network unbalance.

The means for preventing hunting of the system in this arrangement includes a pair of resistances IIh. and I16 connected between the cathodes of valves I63 and I64, and a condenser I'1h connected from the point of engagement of resistances IIh and I16 to the negative ends of resistances I12 and I13. When the potential drops across resistances I12 and I13 are identical, no current will flow through resistances Hit and I 16 and consequently the potential across 'the terminals of condenser I1h will be the same as that across resistances I12 and I13. The potential drop across resistance I13 is applied directly to control the conductivity of valve I45, but the potential drop across resistance 112 controls the conductivity of valve I44 only in so far as it changes the potential on the condenser I1h. Thus, on unbalance of the bridge network, for example, on unbalance in the direction which increases the conductivity of valve I63 and thereby the potential drop across resistance I12, the potential on the condenser will be increased, but due to the flow of current through resistance [In established as a result of the difference in potential drops across resistances I12 and I18, the condenser potential will not assume the final value of potential across resistance I12 while current flows through resistance I Ih. Thus, the full amplified efiect of the bridge network= unbalanced E. M. F. is not immediately applied to the input terminals of valves I and I45, but is delayed in a manner identical to that of the anti-hunting arrangements previously described so that the en-.

ergization of motor Illa is reduced before the contact I62 has been adjusted to the position corresponding to the then value of the resistance I58 whereupon the inertia of the motor will operate to effect the adjustment of contact I56 to the exact balance position. It is noted that by properly proportioning the values or resistances I18 and IIh and condenser I1h, the time required for the condenser to assume the full value of potential across resistance I12 may be made exactly that required for the motor to stop so that when the motor does stop the system will be in exact balance. It is noted further that since the potential across resistance I13 is immediately applied to control the motor rotation the potential drop across resistance I13 may temporarily exceed that across condenser I1h to thereby effect energization of the motor for rotation in the opposite ,direction and consequently fast deceleration of the motor as in the previous arrangements described.

It will be apparent the motors III, Ila, or Ilb of the various embodiments of our invention disan original electromotive force to be measured,.

closed herein may be employed to operate a control valve for controlling the supply of heating agent to a furnace to the temperature of which a thermocouple is responsive, or another motor desirably operated together with any of the above mentioned motors may be so employed. For example, as shown in Fig. 19, a furnace I11 to the heat of which a thermocouple is responsive is heated by a resistance I18 which is connected to electric supply conductors L and L, through a rheostat I19, the adjustment of which is ef,-

fected by a motor I80. The motor I88 may be exactly like motor III, for example, and is connected in parallel therewith. The mechanical connection of the rheostat I19 to the motor is such as to increase and decrease the supply of electric current to the resistance I18 as the temperature to which the thermocouple 2 is responsive drops below and rises above a predetermined level.

Certain hunting elimination features disclosed but not claimed herein are disclosed and claimed in a copending application of Thomas R. Harrison Serial No. 263,938 filed March 24, 1939, and issued into Patent 2,312,711 on March 2, 1943.

Other novel subject matter disclosed in Figs. 4, 11 and 15 but not claimed herein is disclosed and is being claimed in an application Serial No. 421.173 filed on December 1, 1941, by Walter P.

Wills, and issued into Patent 2,423,540 on July 4 8, 1947, an application Serial No. 459,638 filed September 25, 1942, byWalter P. Wills, and issued into Patent 2,404,894 on July 30, 1946, and an appl cation Serial No. 459,639 filed by Walter P. Wills on September 25, 1942, and issued into Patent 2.367,914 on January 23, 1945, which subject matter has been divided out of the present application.

While ih accordance with the provisions of the statutes we have illustrated and described the best form of our, invention now known to us it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of our invention as set forth in the appended claims, and that certain features of our invention may sometimes he used to advantage without a corresponding use of other features.

Having now described our invention what we claim as new and desire to secure by Letters Patent is:

1. The method of restoring the balance of an electrical network which comprises the steps of producing a potential in variable accordance with an original electromotlve force in said net work to be measured, opposing said potential to a measuring electromotlve force, measuring the difierence between said potential and said measuring electromotlve force, adjusting said meas- I tween said potential and measuring force is zero.

2. The method of restoring the balance of an electrical network which comprises the steps of producing a potential in variable accordance with opposing said potential to a measuring electromotive force, measuring the difierence between said potential and said measuring electromotlve force, adjusting said measuring electromotlve force by means of the energization of motor means adjusting said measuring electromotlve force in accordance with said measurement to reduce said difference, and varying said potential according to the rate of adjustment of said measuring electromotlve force until the relation between said potential and said original electromotive force is a predetermined value.

3. Measuring apparatus including means for producing a variable electrical effect to be measured, means for producing a standard electrical effect, an electrical network in which saideflects are opposed, a device for varying said standard effect, a motor arranged to adjust said device when energized and having the inertia characteristic which produces further adjustment-of said device following deenergization, means responsive to unbalance in the efiects in said network to selectively energize said motor for rotation in one direction or the other depending upon the direction of said unbalance, and means included in said network to automatically control the opposing of the first mentioned effect to said standard effect in a predetermined manner with respect to time on a change in said first mentioned effect and proportioned to balance said network following a change in said first mentioned effect when the difference between said first mentioned and standard effect is equal to the effect produced by said device under control of said motor following deenergization of the latter.

4. Measuring apparatus including means for producing a variable electromotive force to be measured, means for producing a standard electromotive force, a network in which said electromotive forces are opposed, a device for varying said standard electromotive force, a motor arranged to adjust said device, means responsive to unbalance in the electromotive forces in said network to selectively energize said motor for rotationin one direction or the other depending upon the direction of said unbalance, and means included in said network to automatically control the opposing of the first mentioned electromotive force to said standard electromotive force in a predetermined manner with respect to time on a change in said first mentioned electromotive force and proportioned to balance said network following a change in said first mentioned electromotive force when the difference between said first mentioned and standard electromotive force is equal to the electromotive force produced by said device under control of said motor following deenergization of the latter.

5. Measuring apparatus including means for producing a variable electrical efiect to be measured, means for producing a standard electrical effect, a device for varying said standard effect, means for opposing said effects, including means to delay the complete application of the change in said first mentioned efiect to said standard effect in accordance with the actuation of said device, means responsive to the unbalance of said effects, and a motor under control of said last mentioned means for adjusting said device.

6. In measuring apparatus, a normally balanced electrical network including means to variably unbalance said network and means responsive to unbalance of said network, a member movable to rebalance said network, a device having inertia and controlled by said means to operate said member, and electric capacity reactance means in said network controlling the un-- balancing effect of said first mentioned means to compensate for the inertia of said device as required to prevent hunting of said member.

7. The combination of claim 6 wherein said last mentioned means includes a. condenser and "last ment oned means includes a condenser and a resistance.

9. The combination of claim 6 wherein said last mentioned means includes a condenser and a resistance connected in parallel relation.

10. The comb nation of claim 6 wherein said last mentioned means includes a condenser.

11. Control apparatus including means for producing a variable electromotive force to be measured. an adjustable member having inertia and adapted to be moved in accordance with the magnitude of said electromotive force, means to adjust said adjustable member, means responsive to the magnitude of said electromotive force to control said adjusting means, and 'a connection to applysaid electromotive force to said control means, said connection including stationary means therein controlling the application 01 said electromotive force to prevent hunting of said member.

12. The combination of claim 11 wherein said stationary means includes a condenser and an impedance associated with said condenser.

13. The combination. of claim 11 wherein said stationary means includes a condenser and a resistance associated with said condenser.

14. The combination of claim 11 wherein said stationary means includes a condenser and a resistance connected in parallel relation to said condenser.

15. The combination of claim 11 wherein said stationary means includes a condenser.

' 16. Apparatus for measuring a variable condition including means for producing said variable condition. means for producing a unidirectional electromotive force of magnitude varying with the magnitude of said condition, an adjustable member having inertia to indicate the magnitude of said condition, means to adjust said adjustable member, means responsive to the magnitude of,

said adjusting means, and a connection to supply said electromotive force to said control means, said connection including a condenser and resistance therein operating to delay the application of said electromotive force to said control means and thereby to prevent hunting of said member.

17. The combination of claim 16 wherein said condenser and resistance are connected in series 1relation across said unidirectional electromotive orce.

18. The combination of claim 16 wherein said condenser and resistance are connected in parallel relation.

19. Apparatus for measuring a variable condi-. tion including means for producing said variable condition, means for producing a source of unidirectional electromotive force of magnitude varying with the magnitude of said condition, an

adjustable member having inertia to indicate the magnitude of said condition, means to adjust said adjustable member, means responsive to the magnitude of said unidirectional electromotive forceto control said adjusting means, a pair of conductors on which said electromotive force is applied and connected to said control means, and means for preventing hunting of said member including a resistance connected in one of said conductors and a condenser connected from the end of said resistance remote from said source to the other of said conductors.

20. A high speed recorder for recording the variations in an unknown electromotive force under measurement including a source of known electromotive force to which said unknown electromotive force is opposed by a conductive connection, means to vary the magnitude of said known electromotive force, a device responsive to an effect tending to equal the differential between said electromotive forces to control said means, and stationary means in said conductive connection to delay the equalization of said effect and said differential to prevent hunting of said device.

21. A high speed recorder for recording the variations in a unidirectional E. M. F. under measurement including a source of known unidirectional electromotive force to which said unknown electromotive force is opposed by a conductive connection, means to vary the magnitude of said known electromotive force, a device under control of the differential between said electromotive force to control said means, and stationary means in said conductive connection introducing a time delay in the application of a change in said unknown electromotive force to said known electromotive force to prevent hunting of said device.

22. A high speed measuring system comprising a potentiometer network, means for producing an unbalanced electromotive force in said network, an impedance adjustable to rebalance said network, a device for adjusting said impedance, relay means responsive to said unbalanced electromotive force for controlling said device, and means in said network tending to maintain the balance of said network independently of said relay means.

23. In measuring apparatus, a normally balanced unitary network including means to unbalance said network and means responsive to unbalance of said network, a member movable to rebalance said network, a device controlled by care:

27 said second mentioned means for operating said member, and means in said network tending to maintain the balance of said network independently of said second mentioned means.

24. A measuring system comprising a potentiometric network, said potentiometric network including an adjustable resistance, a second resistance, and a pair of conductors for impressing a source of unidirectional electromotive force on said resistances, a resistance in one of said conductors and having a value substantially higher than the sum of said adjustable resistance and said second resistance, 'a condenser associated with said third mentioned resistance, a member having inertia to adjust said adjustable resistance, and means connected to said second mentioned resistance to control the adjustment 'of said member. said third mentioned resistance and condenser operating to prevent hunting of said member.

25. A measuring system comprising a potentiometric network, said potentiometric network including an adjustable resistance, a galvanometer coil, and a pair of conductors for impressing a source of unidirectional electromotive force on said resistance and galvanometer coil, a resistance in one of said conductors and having a value substantially higher than the sum of resistances of said first mentioned resistance and said galvanometer coil, a condenser associated with said second mentioned resistance, a member having inertia to adjust said adjustable resistance, and means under control of said galvanometer coil to control the adjustment of said member, said second mentioned resistance and condenser operating to preventing hunting of said member.

26. The method of restoring the balance of an electrical network which comprises the steps of producing a potential in variable accordance with an original electromotive force in said 'network to be measured, said potential being substantially equal to said original electromotive force to be measured when said network is balanced but being different from said original electromotive force to be measured when said-network is unbalanced, opposing said potential to a measuring electromotive force, -measuring the difference between said potential and said measuring electromotive force, adjusting said measuring electromotive force by means of the energize.- tion of motor means adjusting said measuring electromotive force in accordance with said measurement to reduce said difference, adjusting said potential in value toward the value of said original electromotive force to be measured in accordance with the adjustment of said measuring electromotive force, and continuing the energization until the difference between said potential and measuring force is zero.

27. The method of restoring the balance of an electrical network which comprises the steps of producing a. potential of a value intermediate the value of an original electromotive force in said network under a condition of balance and a value of saidelectromotive force in a condition of network unbalance, opposing said potential to a measuring electromotive force, measuring the difference between said potential and said measuring electromotive force, adjusting said measur Number 28 ing electromotive force by means of the energize.- tion of motor means adjusting said measuring electromotive force in accordance with said measurement to reduce said difference and adjusting said potential in value toward said unbalanced value of said original electromotive force in accordance with the adjustment of said measuring electromotive force, and continuing the energization until the difference between said potential and measuring force is zero.

28. Measuring apparatus including means for producing a variable electrical effect to be measured, means for producing a standard electrical effect, a device for varying said standard effect,

' electrical connections between said means for opposing said effects, means connected in said electrical connections to delay the complete application of the change in said first mentioned effect to said standard effect in accordance with the actuation of said device, means responsive to the unbalance of said effects, and a motor under control of said last mentioned meansfor adjusting said device.

29. Control apparatus including means for producing a variable electromotive force to be meas-- ured, an adjustable member having inertia and adapted to be moved in accordance with the magnitude of said electromotive force, means to adjust said adjustable member, control means responsive to the magnitude of said electromotive force to control said adjusting means, and aconnection to apply said electromotive force to said control means, said connection including stationary means therein controlling the application of said electromotive force to said control means in accordance with the extent to which said adjustable member is adjusted to prevent hunting of said member.

30. A high speed recorder for recording the variations in an unknown electromotive force under measurement including a source of known electromotive force to which said unknown electromotive force is opposed by a conductive connection, means to vary the magnitude of said known electromotive force, a device responsive to an effect tending to equal the differential between said electromotive forces to control said means, and stationary electrical means in said conductive connection to which only currents produced by said known and unknown electromotive forces are applied to delay the equalization of said effect and said differential to prevent hunting of said device.

31. A high speed recorder as specified in claim 30 in which said stationary electrical means comprises a condenser and a reactance' THOMAS R. HARRISON.

WALTER P. WILLS.

REFERENCES CITED.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,859,930 Miller May 24, 1932 1,862,595 Holden June 14, 1932 2,105,598 Hubbard Jan. 18, 1938 2,113,436 Williams Apr. 5,1938 

